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The document discusses the testing and analysis of synchronous generators, including calculations for armature resistance, synchronous reactance, and field current requirements under various load conditions. It also examines the effects of connecting additional loads on system frequency and the distribution of power between multiple generators. Key questions are posed regarding generator performance metrics such as speed, power output, and efficiency in different operational scenarios.

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Poula Nahoom
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23 views4 pages

Sheet 1

The document discusses the testing and analysis of synchronous generators, including calculations for armature resistance, synchronous reactance, and field current requirements under various load conditions. It also examines the effects of connecting additional loads on system frequency and the distribution of power between multiple generators. Key questions are posed regarding generator performance metrics such as speed, power output, and efficiency in different operational scenarios.

Uploaded by

Poula Nahoom
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Sheet 1

1. A 2oo-kVA, 480-V 50-Hz, Y-connected synchronous generator


with a rated field current of 5 A was tested, and the following data
were taken:
• VT,OC at the rated If was measured to be 540 V.
• ILSC at the rated If was found to be 300 A.
• When a dc voltage of 10 V was applied to two of the tenninals,
a current of 25 A was measured.
Find the values of the armature resistance and the approximate
synchronous reactance in ohms that would be used in the
generator model at the rated conditions.
2. A 480-V, 60Hz, Δ-connected, four-pole synchronous generator has
the OCC shown in Figure 1. This generator has a synchronous
reactance of 0.1 Ὠ and an armature resistance of 0.015 Ὠ. At full
load, the machine supplies 1200 A at 0.8 PF lagging. Under full -
load conditions. the friction and windage losses are 40 kW. and the
core losses are 30 kW. Ignore any field circuit losses.
i) What is the speed of rotation of this generator?
ii) How much field current must be supplied to the generator to
make the terminal voltage 480 V at no load?
iii) If the generator is now connected to a load and the load draws
1200 A at 0.8 PF lagging, how much fi eld current will be required
to keep the terminal voltage equal to 480 V?
iv)How much power is the generator now supplying? How much
power is supplied to the generator by the prime mover? What is
this machine's overall efficiency?
v) If the generator's load were suddenly disconnected from the line,
what would happen to its terminal voltage?
vi)Finally, suppose that the generator is connected to a load drawing
1200 A at 0.8 PF leading. How much field current would be
required to keep VT 480 V?

3. Figure 2 shows a generator supplying a load. A second load is to


be connected in parallel with the first one. The generator has a no-
load frequency of 61.0 Hz and a slope sp of 1 MW/Hz. Load I
consumes a real power of 1000 kW at 0.8 PF lagging. while load 2
consumes a real power of 800 kW at 0.707 PF lagging.
i) Before the switch is closed. what is the operating frequency of
the system?
ii) After load 2 is connected. what is the operating frequency of the
system?
iii) After load 2 is connected. what action could an operator take
to restore the system frequency to 60 Hz?

4. Figure 3 shows two generators supplying a load. Generator I


has a no-load frequency of 61.5 Hz and a slope Sp of I MW/Hz.
Generator 2 has a no-load frequency of 61.0 Hz and a slope sp of
1MW/Hz. The two generators are supplying a real
load totaling 2.5 MW at 0.8 PF lagging.
i) At what frequency is this system operating, and how much power
is supplied by each of the two generators?
ii) Suppose an additional 1-MW load were attached to this power
system. What would the new system frequency be, and how much
power would G1 and G2 supply now?
iii) With the system in the configuration described in part (ii) ,
what will the system frequency and generator powers be if the
governor set points on G2 are increased by 0.5 Hz?
5.

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